Ignored lava hitbox level

The bug 

The effect for entities swimming in lava ignores the height that the lava actually is. This means that if lava exists in the block space in any form, any entity that enters that block space will take fire damage (via end portal frames, jumping, etc.).

Any entity that enters that same space at the same height of a stonecutter will be capable of swimming upwards and take lava damage (via slabs, stairs, lanterns, stonecutter, jumping, etc.).